137 - Adaptive Radioresistance in Muscle-Invasive Bladder Cancer Is Driven by Tumour-Microenvironment Co-Evolution and Enables Biomarker-Guided Radiotherapy

Purpose/Objective(s): Radiotherapy (RT) enables bladder preservation and cure in muscle-invasive bladder cancer (MIBC), yet treatment failure from radioresistance remains a major barrier to improved outcomes and treatment personalization. Radioresistance is commonly viewed as a fixed tumor-intrinsic phenotype, however, RT imposes selective pressures that may drive adaptive tumor–microenvironment (TME) evolution. We hypothesized that radioresistance represents a dynamic, treatment-induced biological state shaped by hypoxia, extracellular matrix (ECM) remodeling, and tumor plasticity. We integrated experimental modelling with multi-omics to define mechanisms and clinically actionable biomarkers of adaptive radioresistance.

Materials/Methods: Radioresistant phenotypes were generated across multiple bladder cancer cell lines using fractionated irradiation (2.75Gy daily - 4weeks). RNAseq with network analysis identified coordinated biological programs associated with resistance. CRISPR-Cas9 perturbation experiments interrogated hypoxia-regulated pathways governing radiation response. To model physical TME effects, tumor cells were cultured within a 3D self-assembling peptide hydrogel with tunable stiffness exposed to graded radiation doses and assessed by viability and proliferative recovery. Clinical translation incorporated integrated analyses of transcriptional hypoxia signatures, copy number variation (CNV), tumor transcriptomics, and plasma proteomics across public and retrospective MIBC RT cohorts.

Results: Independent systems converged on adaptive programs characterized by cytoskeletal reorganization, ECM interaction, and cellular plasticity. A 29-gene signature distinguishing radioresistance was enriched for actin filament organization (p = 0.0019). Network analyses identified highly connected intramodular hubs implicating microenvironmental signaling as a central determinant of radiation response. In 3D models, ECM stiffness significantly reshaped radiation sensitivity in a dose-dependent manner, demonstrating active microenvironmental modulation of therapeutic susceptibility. Across clinical cohorts, hypoxia associated with radioresistance and increased tumor CNV burden. Longitudinal plasma proteomics revealed dynamic ECM and immune pathway remodeling, with circulating signatures correlating with treatment response and demonstrating predictive potential.

Conclusion: Radioresistance in MIBC represents an adaptive biological state arising from tumor–microenvironment co-evolution under RT selection pressure. Integrating mechanistic experimentation with clinical multi-omics identifies actionable pathways and circulating biomarkers enabling biologically adaptive radiotherapy and supporting biomarker-guided treatment personalization.